The present invention relates to injection molding machines, and in particular, to a valve for an injector nozzle on an injection molding machine adapted to prevent the stringing of thermoplastic residue from the nozzle.
Injection molding is a manufacturing process in which heated thermoplastic is forced under pressure into a mold to produce a part. The heated thermoplastic is delivered at relatively high temperatures and under high pressure from an injector. After cooling, the hardened part is removed from the cavity of the mold and the operation is repeated, normally cycling the mold repeatedly to make one part after another.
For two-shot and other sophisticated molding operations, the injector may be separated from the mold to permit mold movement or exchange. During this period of separation, heated thermoplastic may undesirably “string” from the injector nozzle. To avoid this problem, the injector may include a valve in communication with the nozzle and adapted to regulate the dispensing of the injection thermoplastic. Such valves may be automatically configured to turn the flow of thermoplastic on and off by using a pressure sensitive check valve or by mechanical actuation of a valve lever tied to the injection molding machine mechanism.
In this latter design, pressurized thermoplastic material can undesirably leak along the path of the valve operator producing a problem similar to that of the stringing and or preventing free operation of the valve mechanism as a result of contamination.